It was clear here in Chelmsford last night almost up to astronomical
darkness when clouds arrived so I managed to get wide and narrow field
images of the comet. The widefield image in colour is here:

https://britastro.org/observations/observation.php?id=20241025_063719_c5dad64fafe03944

I've used the green channel of this image to get a magnitude using
comphot but it is at the low end of what visual observers are getting.
Comphot gives 5.5 with a coma diameter of 15.5 arcmin. The visual
observations on COBS for last night are 4.7 - 5.2.

My question for visual observers is how do you eliminate the tail from
your magnitude estimate? This is a very dusty comet and it is not
obvious where the coma ends and where the bright inner tail starts.
Comphot does this automatically, and possibly wrongly in this case, by
assuming that the coma is symmetric around the photocentre. The image
shows the photometric aperture that comphot used in this case.

Nick.